1. Field of the Invention
The present invention relates to a pneumatic tire provided with a tread pattern on which a plurality of blocks are formed with circumferential grooves, which extend in a circumferential direction of the tire, and lateral grooves.
2. Description of the Related Art
As a pneumatic tire which secures driving performance on a snowy road without forming a sipe in a block, a pneumatic tire provided with a tread pattern shown by FIG. 8 or FIG. 9 is known. Such a pneumatic tire commonly has 4 to 6 circumferential grooves 1 that extend along a circumferential direction of a tire, and has relatively small blocks 10 partitioned by the circumferential grooves 1 and lateral grooves 2.
However, such a pneumatic tire has relatively small blocks, and therefore the blocks are apt to be deformed. This caused a problem of easy occurrence of toe and heel wear. Also, against a backdrop of the market, a demand on driving performance on a snowy road has been changing and economical efficiency (improvement of wear and irregular wear resistance) has become much important as a result of repletion of studless tires (improvement of driving performance on a snowy and icy road) and improvement in road surface conditions, and accordingly, a configuration that meets the above demand is being sought. That is, a demand on driving performance on a snowy road for a winter tire has been being specialized in driving performance on a road covered with shallow snow, and a demand for a tread pattern has been radically changing from a conventional tread pattern required shear force in the snow into a tread pattern required a scratching effect by an edge line of a block.
Also, there is a problem such that when relatively small blocks are formed on a tread edge region, deformation against action force upon evolution increases and evolution performance decreases.
Therefore, in Japanese Unexamined Patent Publication (Kokai) No. 10-86613, a pneumatic tire is proposed on a purpose of securing cornering force upon evolution, wherein lateral thin groove with a shallow bottom is formed between blocks on a tread edge region, a sipe is formed on the groove bottom of the lateral thin groove, and the sipe extends along the lateral thin groove and also has a discontinuity. Also, in the block on the tread edge region, a land portion sipe, which is a sublinear land portion sipe and is disposed to be subparallel to the above sipe, is disclosed.
However, in a tire described in Japanese Unexamined Patent Publication (Kokai) No. 10-86613, a groove width of the groove bottom sipe formed on the lateral thin groove was narrow, and therefore sufficient edge effect could not be exhibited when a tire wore out, and it was particularly hard to say that driving performance on a road covered with shallow snow was good enough. Also, there was a problem such that when a groove bottom sipe with both closed ends was formed on the groove bottom of the lateral thin groove having a shallow bottom, suppression effect on irregular wear was little, since the width of the lateral groove was narrow, the depth was shallow and the groove width of the groove bottom sipe was narrow, so as to decrease effect by virtue of the groove bottom sipe.